Excellent deliverability, instant sending, powerful API, complete email analytics (opens, clicks, bounces) fast support It's straightforward to set up; I barely used the documentation. Also, their KYC process is flawless and quick; I was able to use the full features only a couple of hours after signing up. They have a great dashboard with a vast amount of valuable data about the emails sent, very well organized, and with powerful filter functions. I contacted support once to ask for the availability of a feature (SMTP relay) and got a friendly answer within mere hours. They implemented SMTP relay a couple of days later. The API is very fast to accept emails, and Sent-to-Inbox time is almost instantaneously, which is very important when sending password reset emails etc. MailerSend's free tier is beyond generous, their regular pricing is very affordable. I recommend trying them out if you are looking for a transactional email provider or transactional SMTP relay.

Super easy to use API for dev. Easy to use mail templating for designer. I love the fact that we can define data from the dashboard and simply call with the API from backend to easily send email. Dev don't need to do design, and designer don't need to code as well. It's awesome. Very clear dashboard for tracking errors and mail bounce. And adding to that a very generous free tier !